Process for preparing a metal plate receptive to a decorative metal deposit

ABSTRACT

IN ACCORDANCE WITH CERTAIN OF ITS ASPECTS, THIS INVENTION RELATES TO NOVEL COMPOSITIONS AND TO THE PROCESS FOR PREPARING A METAL PLATE RECEPTIVE TO A DECORATIVE NOBLE METAL DEPOSIT, CHARACTERIZED BY THE PRESENCE OF MICROPOROUS AREAS AND MICROCRACKED AREAS OVER SUBSTANTIALLY THE ENTIRE SURFACE OF SAID NOBLE METAL PLATE, WHICH COMPRISES AFFIXING TO A BASIS MATERIAL BEARING A CONDUCTIVE METAL SURFACE A STRATUM OF PARTICLES HAVING A PARTICLE SIZE OF ABOUT 0.05-15 MICRONS AND A DENSITY ON SAID CONDUCTIVE METAL   SURFACE OF ABOUT 100-5,000,000 PARTICLES/CM.2, AND DEPOSITING IN SAID STRATUM OF PARTICLES A CONDUCTIVE METAL LAYER HAVING AN EFFECTIVE THICKNESS LESS THAN THE MAXIMUM THICKNESS OF SAID STRATUM OF PARTICLES THEREBY FORMING A MATRIX WHEREIN SAID PARTICLES ARE RETAINED AFFIXED TO SAID SURFACE IN FIXED POSITION IN SAID CONDUCTIVE METAL LAYER, AND AT LEAST SOME OF SAID PARTICLES INTERCEPT THE SURFACE OF SAID CONDUCTIVE METAL LAYER.

Apnl 6, 1971 H. CHESSIN- 3,574,068

' PROCESS FOR PREPARING A METAL PLATE RECEPTIVE T0 A DECORATIVE METALDEPOSIT v -Fi1ed Nov. 23, 1965 INVIZNTUR.

H YMA/v CHESS/N BY C424 6. JEUTTER AI'I'OQA/E) United States Patent US.Cl. 20416 20 Claims ABSTRACT OF THE DISCLOSURE In accordance withcertain of its aspects, this invention relates to novel compositions andto the process for preparing a metal plate receptive to a decorativenoble metal deposit, characterized by the presence of microporous areasand microcracked areas over substantially the entire surface of saidnoble metal plate, which comprises affixing to a basis material bearinga conductive metal surface a stratum of particles having a particle sizeof about 0.0545 microns and a density on said conductive metal surfaceof about 1005,000,000 particles/cm. and depositing in said stratum ofparticles a conductive metal layer having an effective thickness lessthan the maximum thickness of said stratum of particles thereby forminga matrix wherein said particles are retained affixed to said surface infixed position in said conductive metal layer, and at least some of saidparticles intercept the surface of said conductive metal layer.

This invention relates to a novel process for preparing a metal plateparticularly characterized by its receptivity to noble metal plate,typified by a corrosion-resistant decorative electrodeposited chromiumplate containing microcracked areas and microporous areas oversubstantially the entire surface of said chromium plate.

As is well known to those skilled in the art, decorative noble metalplate typified by chromium plate may be obtained by e.g.electrodepositing chromium onto a surface of electrodeposited nickel.However chromium plate obtained in this manner may be subject to defectsincluding gross cracking or crazing and excessive corrosion whichdecreases usefulness as decorative chromium.

Prior art processes have attempted to overcome the problem of grosscracking in chromium plate by including in the nickel plating bath (fromwhich may be deposited the nickel undercoat for the chromium plate) asubstance which produces a microporous condition in the chromium platesubsequently deposited.

However prior art methods have not succeeded, by employing additives inthe nickel plating bath, in preventing gross cracking over all areas ofthe subsequently deposited chromium plate and thus it has not beenpossible to attain a chromium plate characterized by the presence ofmicrocracked areas and microporous areas over substantially the entiresurface of said chromium plate.

It is an object of this invention to permit attainment of a plateparticularly characterized by its receptivity to a noble metal platetypically a decorative chromium plate. It is a further object of thisinvention to provide a chromium plate which is highly useful as adecorative chromium plate, and which contains microcracked areas andmicroporous areas over substantially the entire surface area of saidchromium plate. Other objects will be apparent to those skilled in theart from inspection of the following description.

"ice

In accordance with certain of its aspects, the process of this inventionfor preparing a metal plate receptive to a decorative noble metaldeposit, characterized by the presence of microporous areas andmicrocracked areas over substantially the entire surface of said noblemetal plate, comprises affixing to a basis material bearing a conductivemetal surface a stratum of particles having a particle size of about0.05-15 microns and a density on said conductive metal surface of about5,000,000 partic1es/cm. and depositing in said stratum of particles aconductive metal layer having an effective thickness less than themaximum thickness of said stratum of particles thereby forming a matrixwherein said particles are retained affixed to said surface in fixedposition in said conductive metal layer, and at least some of saidparticles intercept the surface of said conductive metal layer.

The basis material which may be treated according to this invention mayinclude a basis metal such as iron, steel, zinc, or brass which has beenfirst plated with a nickel, etc., either pure or in the form of alloy.The preferred basis metal to be plated in accordance with this inventionmay be steel, zinc, or brass and most preferably steel, zinc, or brasswhich has been first plated with a conductive deposit such as a plate ofbright nickel, typically preceded by a first plate of copper, bronze, orsemi-bright nickel.

Other basis materials which may be treated by the process of thisinvention may include plastics and resins includingacrylonitrile-butadiene-styrene, acetals, acrylics, alkyds, allyls,aminos, cellulosics, chlorinated polyethers, epoxys, furanes,fiuorocarbons, isocyanates (urethanes), polyamides (nylons), phenoxys,phenolics, polycarbonates, polyesters, polyethylenes, polypropylenes,silicones, polystyrenes, polyvinyls, and copolymers, etc. of thesematerials. When the basis material to be treated by process of thisinvention is a plastic or resin, the surface thereof will be treated asby deposition thereon of a conductive deposit, such as a nickel deposit.

The basis material bearing a conductive surface, preferably a brightnickel plate, may be immediately treated after disposition of such plateor it may be water rinsed; or it may be rinsed, dipped in aqueous acidsolution such as O.5%-10%, say 2%, by weight of sulfuric acid prior tofurther treatment. The so-treated material may be dried or it may befurther treated as is. If drying has been permitted, the conductivesurface may be cleaned as by cathodically treating in alkaline cleanerfollowed by rinsing in water or dipping in an acid solution beforefurther treatment.

Nickel plating baths which may be employed in the practice of thisinvention in forming plate on the surface of the basis material mayinclude various electrodeposition baths. Typical baths may include thoseindicated below, all values being grams per liter (g./l.), except forthe pH which is electrometric.

A typical Watts bath which may be used in practice of this invention mayinclude baths containing the following components in aqueous solution:

A typical sulfamate-type bath which may be used in practice of theprocess of this invention may include the following components inaqueous solution:

TAB LE II Component Minimum Maximum Preferred Nickel sulfamate 330 400375 Nickel chloride, hydrated 15 60 45 Boric acid 33 55 45 pH 3 5 4.

A typical chloride-free, sulfate-type bath which may be used in practiceof the process of this invention may include the following components inaqueous solution:

TAB LE III Component Minimum Maximum Preferred Nickel sulfate, hydrated300 500 400 Boric acid 35 55 45 pH 3 5 4. 0

A typical chloride-free, sulfamate-type bath which may be used inpractice of the process of this invention may include the followingcomponents in aqueous solution:

TAB LE IV Component Minimum Maximum Preferred Nickel sulfamate 300 400350 Boric acid 35 55 45 pH 3 5 4. 0

A typical pyrophosphate-type which may be used in practice of theprocess of this invention may include the following components inaqueous solution:

A typical fluoborate-type bath which may be used in the practice of theprocess of this invention may include the following components inaqueous solution:

TABLE VI Component Minimum Maximum Preferred Nickel fiuoborate,hydrated- 250 400 300 Nickel chloride, hydrated.-. 15 60 30 Boric acid15 30 20 pH 2 4 3. 0

It will be apparent that the above baths may contain components inamounts falling outside the preferred minima and maxima set forth, butthat most satisfactory and economical operation may normally be effectedwhen the components are present in the baths in the amounts indicated.

The plating baths may further contain brighteners or other additivessuch as sodium saccharate or wetting agents. High-foaming wetting agentssuch as sodium lauryl sulfate may be particularly useful when employedin conjunction with mechanical agitations; and low-foam ing agents suchas sodium dialkylsulfosuccinates may be particularly useful whenemployed in conjunction with air agitation.

In practice of this invention, the basis material preferably bearing afirst plate (of e.g. copper) and a nickel or duplex nickel plate, may befurther treated by afixing thereto a stratum of particles having aparticle size of about 0.05-15 microns.

Typically the particles may be finely-divided, naturallyoccurring orartificially prepared materials. They may be spherical, chunky, angular,ovular, elongated, plateletshaped, etc. Preferably they may be flat,i.e. have two dimensions substantially greater than the third dimension.The preferred particles may be platelets.

Typical particulate materials which may be employed may include talc;kaolin; wax; graphite; sulfides such as molybdenum disulfide andtungsten disulfide; pigments including barytes, chromium-cobalt greenand cobalt-aluminum blue and oxides such as silica and alumina;particles of plastic e.g. polymers or copolymers of styrene, butadiene,acrylonitrile, vinyl acetate, vinyl chloride, etc.; diatomaceous earths;powdered aluminum; activated carbon; silicates e.g. sodium silicate;carbonates, e.g. calcium carbonate; carbides; sulfur; etc., or mixturesof these materials.

There may also be present other additives such as polar organiccompounds, e.g. amides, amines, long-chain alcohols, acetylenics, etc.,to enhance the properties of adhesion, inhibition, or dispersion.

Application of particles may be effected by contacting the basismaterial with particles. The particles may be blown over the surface ofthe conductive metal surface of the basis material. The basis materialmay be dipped into a bed, preferably a fluidized bed of particles i.e.particles suspended in an upflowing stream of gas. Afiixing of particlesmay be effected by electrostatic or electrophoretic techniques on thebasis metal piece. If desired, the basis metal may be wet to assistdeposition thereon and adherence thereto of the particles.

The preferred particles may be used in the form of a bath i.e. asuspension, emulsion, dispersion, or latex of the solid or semi-solidparticles in a fluid, preferably a liquid. In one preferred embodiment,the particles may be particles of solid suspended in a liquid inconcentration as low as 0.001%, typically, 0.1%-2%, and preferably about0.5%. Outstanding results may be obtained by use of baths containing0.1%2% particles.

Typically the particles in the bath may be from commercially availablematerials: for example, talc may be. obtained having particles rangingin size up to about 7 microns. 0.0l2% of talc may be added to water anddispersed as by milling in a ball mill or in a Waring Blendor or bystirring. Similar techniques may be employed to disperse wax, pigments,kaolin, etc.

The fluid, typically aqueous medium, in which the particles may besuspended may be water, but preferably is a bath having a compositionsubstantially similar to the bath immediately preceding from which thebasis material may have been removed after treatment, e.g. a water-rinsebath or a nickel-plating bath.

Air, mechanical, or ultrasonic agitation may be used to maintain theparticles in suspension. Additives such as suspending agents includingsurfactants, dispersants, thixotropes, emulsifiers, etc., e.g.alginates, lignosulfonates, gelatin, etc., may be present, and ifdesired, electrolytes including sodium sulfate, heavy metal salts,acids, etc.

When the bath is a latex bath, it may be formed from various resins.Illustrative resins which may be present in latices used in the instantinvention include resins containing non-aromatic unsaturation in therepeating unit of the molecule formed from:

(a) Diene compositions including butadiene typically natural rubber;isoprene i.e. Z-methyl butadiene; chloroprene i.e. 2-chloro-butadiene;pentadiene-1-3; etc.

(-b) Acrylate compositions including acrylate and methacrylate esterssuch as methyl acrylate; methyl methacrylate; ethyl acrylate; ethylmethacrylate; propyl acrylate; etc.

(o) Acrylonitrile compositions including acrylonitrile;methacrylonitrile; ethacrylonitrile; etc.

((1) Vinyl compositions including vinyl chloride; vinyl acetate;l-chloro-propene-l; styrene; 0-, m-, and p-methyl styrenes; etc.

(e) Olefin compositions including ethylene; propylene; butylene; etc.

Typical compositions may include those formed from more than one of theabove types, such as from two components including butadiene-styrene;butadiene-acryloniq trile; methyl acrylate-styrene; etc. or threecomponents (terpolymers) including e.g. acrylonitrile-butadiene-styrene;etc. Most preferably polymers of the noted compositions may be used inthe form of copolymers with e.g. other noted compositions.

The above compositions may be modified and typically carboxylic-modifiedi.e. the molecule containing aliphatic unsaturation may be modified bythe addition thereto of a carboxylic acid group. Typically this may beeffected e.g. by reacting the composition with maleic anhydride in orderto form carboxylic groups on the polymer molecule or by hydrolyzing a CNgroup to a carboxyl group.

It is a feature of the latices which may be employed in practice of theprocess of this invention that they may be readily available fromnatural sources e.g. natural rubber latex or that they may readily beformed by dispersing synthetic compositions in aqueous media, e.g.butadiene-styrene polymer latices.

Illustrative specific commercially available synthetic latices which maybe used in practice of this invention include:

(a) A water-based acrylic polymer latex having a nonionic emulsifier, apH of 7, and an average particle size of 0.16 micron (such as that soldunder the trademark Hycar 2601 by B. F. Goodrich Chemical Co.);

(b) A water-based copolymer of butadiene-styrenecarboxylic modifiedlatex (i.e. a latex wherein butadienestyrene copolymer is modified bythe inclusion of COOH groups), including a synthetic emulsifier, a pH of9, and an average particle size of 0.16 micron (such as that sold underthe trademark Pliolite 491 by Goodyear Industrial Products Co.);

(c) A water-based hydrocarbon resin latex having a nonionic emulsifier,a pH of 8.8 and a maximum particle size of 1 micron (such as that solidunder the trademark Piccopale N-3 by Pennsylvania Industrial ChemicalCorporation);

(d) A water-based vinyl acetate polymer latex having a non-ionicemulsifier, a pH of 4.0-5.5, and an average particle size of about 1micron (such as that sold under the trademark Plyamul 40-370 byReichhold Chemical Co.);

(e) A Water-based vinyl acetate polymer latex having an anionicemulsifier, a pH of 3.5-5.5, and an average particle size of 0.5 micron(such as that sold under the trademark Gelva T S-30 by Shawinigan ResinsCorp.);

(f) A. water-based copolymer of butadiene-styrene 50/50 latex having asynthetic emulsifier, a pH of 9.6, a non-staining anti-oxidant, and anaverage particle size of 0.6 micron (such as that sold under thetrademark Pliolite 176 by Goodyear Industrial Products Co.);

(g) A water-based vinyl chloride polymer latex having a pH of 8.0, andan average particle size of 0.16

micron (such as that sold under the trademark Dow 700 by Dow ChemicalCo.);

(h) A Water-based vinyl acetate polymer latex having a pH of 4.0-5.0, ananionic emulsifier, and a particle size of 005-3 microns (such as thatsold under the trademark CL-102 by Celanese Corp. of America);

(i) A water-based copolymer of vinylidene chloride acrylonitrile 85/15latex having an anionic emulsifier; a pH of 6.0/7.0, and an averageparticle size of 0.2 micron (such as that solid under the trademarkSaran Latex F122 A by Dow Chemical Co.);

The preferred latices may be in the form of nonconductive latices inaqueous medium, typically containing -60%, say resin in the aqueousmedium. Commonly these latices may be characterized by the presence ofcolloidal-size particles, typically less than about one micron andcommonly of the order of 0.0005-0.2 micron. The most highly preferredlatices which may be used in practice of this invention to permitattainment of the preferred chromium plate containing microcracked areasand microporous areas over substantially the entire area of the chromiumplate include the carboxylic-modified butadiene copolymer laticescontaining particles of an average size of up to about 1 micron. Typicalof such latices is (b) supra sold under the trademark Pliolite 491 inwhich the average particle size may be about 0.16 micron. Other laticesmay include vinylidene chloride copolymer latices such as the copolymerwith acrylonitrile, as (i) supra sold under the trademark Saran LatexF122 A15 in which the average particle size may be about 0.2 micron. Apreferred latex may for example be a polyvinyl chloride latex containing0.5% by weight of polyvinyl chloride having a nominal particle sizeabout 0.16 micron, such as that sold under the trademark Dow 700 (g)supra). Additives including dispersants etc. may be present.

Typically the particles may be employed in the form of an aqueousdispersion having the following composition:

Parts by weight Minimum Maximum Preferred A preferred bath in the formof a dispersion which may be employed may include:

Parts by weight Application of the particles onto the metal surface maypreferably be eifected by dipping the metal surface in an aqueous bathcontaining said particles. Dipping may be effected, preferably atambient temperature of 10 C.-40 C., and the surface may be retainedtherein for time sufficient to inundate the surface, typically 5-60seconds, preferably about 30 seconds. Moderate agitation in this stepmay be preferred.

The surface may then be removed from the bath bearing a stratum ofparticles which cling evenly distributed thereonprobably held in placeby surface tension and adsorptive forces. The particles may be affixedto the surface of these forces and may be uniformly distributedthereover. Typically there may be 100-5,000,000 particles on each squarecentimeter of surface, and commonly 5,000-2,000,000 particles/cm? Thesurface so-attained may, if desired, be allowed to dry, or it may bewater-washed, or it may be further processed as is e.g. bearing a thinfilm of adherent liquor.

The surface bearing the stratum of afiixed particles may then be furthertreated. There may be deposited on said surface and in said stratum, aconductive layer having an effective thickness less than the maximumthickness of the stratum of particles whereby a high portion of theupper surfaces of the particles remain uncovered. The surface may beimmersed in a plating bath, preferably an electroplating bath wherein aconductive metal layer may be deposited. The conductive layer maytypically be of nickel, nickel-tin, cobalt, silver, rhodium, platinum,copper, bronze, brass, zinc, cadmium, manganese, etc.; the preferredmetal may be nickel. It is preferred that these baths be continuouslyfiltered, and when necessary, treated with active carbon to preventbuildup of impurities and insolubles.

In the preferred embodiment, nickel may be deposited from any of thebaths hereinbefore noted. Plating may be carried out at 15 C.-60 C., say54 C. The average cathode current density may typically be 1.0-15amperes per square decimeter (a.s.d.), preferably 5 a.s.d. When thepyrophosphate bath supra is used, the temperature s,574,0as

may typically be C.-35 C. and the cathode current density 0.2-2 a.s.d.

Plating may typically be carried out to produce a conductive layerpreferably having an effective thickness less than the maximum thicknessof the stratum of particles whereby said particles are retained in fixedposition in the conductive layer and at least some of said particlespenetrate the surface of the layer. Typically the effective thicknessmay average 0.02-3 microns, preferably 0.2 micron. There will thus beformed a matrix of particles in a conductive layer of metal, i.e. aheterogeneous matrix deposit. Microscopic inspection of the matrixdeposit may readily reveal that the particles may be retained in fixedposition in a matrix of the conductive layer. It will also be observed(as by dark field illumination in a microscope or by the Dubpernelltest) that the particles may traverse the conductive layer and may beobserved above the upper surfaces thereof.

Inspection of the stratum of particles in which the conductive layer hasbeen deposited will clearly indicate that when the conductive layer isdeposited in effective thickness less than the maximum thickness of thestratum of particles, there may be formed a matrix wherein the particlesaflixed to the metal surface are retained in fixed position in theconductive layer and at least some of the particles intercept thesurface of the conductive layer. When the particles in the conductivelayer are substantially spherical particles having more-or-less uniformsize, the resulting matrix cross-section may appear to be essentially asset forth in FIG. 1 of the drawing. Here the effective thickness of theconductive layer may be 50% 60% of the thickness of the stratum ofparticles and the particles more-Or-less uniformly intercept the surfaceof the conductive layer in which they are retained in fixed position.

In FIG. 2, there is shown a typical illustrative crosssection throughthe surface of a conductive layer having an effective thickness lessthan the maximum thickness of the stratum of particles. In this FIG. 2,the particles are heterogeneously sized; as Will be apparent, varyingproportions of different sized particles intercept the surface of theconductive layer in which the particles are retained in position.

In FIG. 3, is shown a typical cross-section of a matrix formed by firstaflixing a plurality of flat platelets of heterogeneous size to thebasis metal and thereafter depositing a conductive layer in the stratum.As will be apparent from inspection of this FIG. 3, the effectivethickness of the conductive layer is less than the actual thickness ofthe stratum of particles, i.e. in spite of the bridging effect, theupper portion or surface of at least some of the platelet particles isnot covered by the deposited conductive layer. It will be noted howeverthat the actual thickness of the conductive layer may be greater thanthe actual thickness of the stratum by as much as half the average widthof the typical platelet particle.

Typically the.actual thickness of the conductive layer which yields aneffective thickness less than the maximum thickness of the stratum ofparticles may vary from typically about 20%-30% of the thickness of thestratum to as much as 200% of the thickness of the stratum. For example,when the particles are irregular or highly porous, the actual thicknessof the conductive layer may be as little as 20%. When the particles aresubstantially spherical and uniformly sized, the actual thickness of theconductive layer may be 50%60%. When the particles are heterogeneouslysized platelets, the actual thickness of the conductive layer may be50%200% or more typically 100% of the maximum thickness of the stratumof particles.

Under each of these conditions, the effective thickness of theconductive layer is less than the maximum thickness of the stratum ofparticles, i.e. the conductive layer forms a matrix wherein theparticles of said stratum are retained in fixed position in theconductive layer and at least some of said particles traverse theconductive layer :and intercept or penetrate the surface of saidconductive layer. In each of these embodiments, it will be observed:that the particles in the matrix remain afiixed to and :appear to be incontact with the metal surface of the basis material.

The product so-prepared may typically thus include :a metal plate(receptive to a noble metal plate, such as :a decorative chromium plate,characterized by the presence of microporous or microcracked areas oversub- :stantially the entire surface of said chromium plate) comprising abasis material bearing a conductive metal surface, and atfixed thereto-5,000,000 particles/emi each particle having a size of about 0.0545microns, said particles being fixed in a matrix containing a conductivemetal layer, at least some of said particles traversing said conductivemetal layer and intercepting the surface thereof.

The basis metal plated with matrix plate, as hereinabove set forth, maythen be further plated with a decorative noble metal deposit, typicallychromium. Chromium plating may be effected at temperature of 30-60 C.,-.say 43 C., and current density of 5-50 a.s.d., say 10 a.s.d., for05-15 minutes, say 5 minutes, from a bath containing 100-500 g./l., say250 g./l., of chromic acid and 1-5 g./l., say 2.5 g./l. of sulfate ion,typically derived from sodium sulfate. Other components including otherchromium plating catalysts, e.g. fluoride or silicofiuoride,self-regulating strontium ion-containing compositions, fumesuppressants, etc. may be present in the chromium plating bath.

The chromium plate prepared by the process of this invention may beobtained in thickness of at least 0.02 micron, typically in decorativethickness of less than about 1 micron, and may be further particularlycharacterized by its bright decorative appearance, its high corrosion-:resistance, and by its microcracked and microporous structure. Thechromium plate, which lies over the matrix plate containing particleswhich may partially protrude above or intercept the surface of theconductive layer, may possess microcracking and microporosity oversubstantially the entire area of its surface.

The microcracked surface area of the chromium plate prepared by theprocess of this invention may be found to have at least 100 microcracksper linear centimeter at 40 mm. from the high current density end of astandard Hull cell panel plated with 10 amperes for 5 minutes at 43 0,compared to 5-10 microcracks per inch for the same chromium on thetypical prior art nickel plate. This unexpectedly high degree ofmicrocracking is sufficient to obtain microcracked areas over allthicknesses of chromium plated in the high and intermediate currentdensity areas. The high degree of microcracking extends sufficientlyover the surface of the chromium plate so as to be essentiallycontiguous with the microporous areas which are characteristic of thelow current density areas of the chromium plate on the matrix surface.

This product may be inspected under a microscope and found to contain amicroporous surface in the low current density areas of the standardHull cell panel. Typically it may possess a plurality of pores,typically about one hundred to tWo or three million (at a chromiumthickness of less than about 0.5 micron), more-or-less uniformlydistributed over the surface of the metal. Chromium deposited, on eg anickel plate, prepared by the process of this invention may thus befound to contain microporous areas or microcracked areas over the entiresurface. Because of the presence, over all areas of the chomium plate,of microperforated areas (i.e. either microporous areas or microcrackedareas), it is possible to attain the novel benefits herein set forth.

When chromium plating is applied .to the heterogeneous matrix-stratumdescribed herein unexpected benefits are derived. Other factors beingconstant, the cracking of a chromium plate will depend on its thickness.Such factors as concentration of chromic acid, concentration of 0.5micron. The degree of microcracking (attained at catalyst materials,temperature of plating, etc.; all have thickness greater than about 0.5micron) over a typical an effect. It is characteristic of prior artchromium dematrix nickel plate may be at least 100 microcracks perposits generally that no cracking appears throughout the li ti t n firstStage of deposition, P to about micfon- AS the 5 In the following seriesof examples, unless otherwise thickness is increased in the undesirablesecond stage, ifi ll noted, basis meta] panels were plated with h rangeof mlcron, gross crackmg may a bright nickel plate in a standardcommercial bright develop; 1n the undeslrable third stage, e.g., about1.0- nickel plating bath The bright nickebplauad panel was 1.5 microns,spangle-type cracking, i.e., microcracking interspersed in grosscracking, may develop. In the fourth stage, microcracking alone maydevelop. The undesirable intermediate stages, i.e., stages two andthree, may be (1). water rinsed, (2) dipped into 2% by weight sulfuricacid, (3) water rinsed, and thereafter (4) dipped into a dispersion bathcontaining the suspended particles desigo'bjectionable in appearance inthe as-plated condition Hated Tflble The basls metal Plate was andparticularly so after the initiation of corrosion has tamed 1n thls bathfor about 30 seconds to form thereon emphasized the presence of thecracks. Micropores and a Stratum of Particles, removed and PasSed to amicrocracks are not objectionable because the fineness of matrix bathwherein a conductive layer of bright nickel structure is not perceivedby the eye except with aid of Plate Was deposited thereofl- The nickelPlating bath magnification. Furthermore the presence of these micro-(treated fI'OIIl time to time active carbon and filtered perforationsover the entire plate, permits attainment of to maintain the solutionfree of impurities and insolubles) the outstanding corrosion-resistantproperties hereinafter Contained 300 g. of nickel sulfate heptahydrate,60 g. of set forth. nickel chloride hexahydrate, 45 g. of boric acid,and

It has been unexpectedly found in the practice of this Water to Blake upP "P invention that microporosity is produced in stage one After mckelPlatmg, Panel was rinsed with and microcracking is facilitated so thatthe undesirable W and then Chromlum Plated in a bath Containstages twoand three Le gross and spangle type cracking, 20 mg 250 g./l. of chromicacid, 2.5 g./l. of sulfate (added do not appear. Thus a final platedchromium part may as Sodlum Sulfate) at 430 have microporosity where lowcurrent densities occur Table VII sets forth the dispersed materialemployed. and microcracking in higher current density areas with TableVI'II sets forth the dispersant, details of operation no objectionablegross cracking or spangle. and results. The footnotes to Table VII andTable VIII The preferred thickness of the bright decorative elecindicatevariations in the standard procedure. The foottroplated chromium platemay be 0.025.0 microns, say notes follow Table VIII.

TABLE VII Percent Designation of Nominal particle Example Type ofdispersed material (w./w.) dispersed material Supplier size (microns) 1gatexiiolyvinyl chloride 0. 5 Dow 700 Dow Chemical Co 0.16. 2 on o 2".--gatetx-piolyvinyl acetate. 0. 027 Plyamul -370 Reichhold Chemical Inc0.5 to 2.0.

1 on re 5 3 Latex-polyvinyl acetate 0. 027 Plyamul 40-370 ReichhpldChemical Inc- 0.5 to 2.0 6 do 0. Gelva 'IS-30. Sliawinlgan Plastics Corp.5. 7 do 0. 55 Shawimgan Resins Corp. O 5. 8 Latex-styrene/butadiene- 0.024 Firestone Plastics Co- 0 2 9 4 Control 10 MOS; powder 1. 0Consolidated Astronautics Incl 11 WSz powder 1.0 Bemol, Ine 0.4. 12 d 1.0 do 0.4. 13 Talc- 0. 8 Sierra Talc & Chem 0.4 to 6 maximum. 14 do 0.8do Do. 15 do 0. 8 0 Do.

16 4 Control 17 Graphite 1. 0 10 to 12 maximum.

d 1. 0 Do. do 1. 0 4.2 maximum. .do 0.1 2t0 5.

do- 0. 4 Do. do 1. 6 Do.

tivated carbon 1. 0 do 1. 0 do 1. 0 Chromiumcobalt pigment. 1. 0 0.5maximum. do 1.0 ....do o. Cobalt-aluminum pigment. 1. 0 V-3285- -do D0.do 1.0 V-3285... do Do. 30 WSz powder-l-Cr-Co pigment 1. 0 SubmicronWS2andV-7687.-. Bemol, Inc. and Ferro Corp 0.4 (W82) and 0.5 maximum(Cr-Co). 31 do 1.0 do do Do.

1. Aldosterse 00-200 Glyco Chem. Inc

...' 1.0 to 6 maximum.

. D Do. 0.4 do.. do Do. 0. 2 Camel-Wh1te Harry T. Campbell Sons Corp. 10maximum. 0. 03 Prepared by pouring hot, saturated alcohol solution ofsulfur into water 1 N o dip in dispersion.

3 Directly to chromium plate from basis nickel plate.

2 Eliminate steps (1), (2), and (3) in standard sequence. 4 Directly tochromium plate from basis nickel plate.

TABLE VIII Matrix bath Chromium Bath Number of Chromium Aqueous phaseTime CD Time C.D Number of microcracks thickness, Example (dispersant)(sec.) (a.s.d.) (sec.) (a.s.d.) pores/em! per cm. microns 1 Electrolytelike 60 0. 65 6O 3. 25 5, 000 0. 032

matrix. 2 60 3. 25 0.032 3 Electrolyte like 180 4. 0 60 20 7, 000 0. 20

matrix. I 4 Z 60 20 0. 20 5 3 Electrolyte like 180 4. 0 60 0. 20

matrix.

4. 0 60 20 0. 20 1. 3 60 6. 5 0. 065 1. 3 60 6. 5 0. 065 60 6. 5 0.065 1. 3 60 6.5 0. 065 7. 0 60 0. 35 2. 0 60 10 0. 10 10 60 0. 50 7. 035 0. 35 l. 3 60 6. 5 0. 065 60 50 0. 50 7. 0 60 35 O. 035 2. 9 60 14. 50. 014 5. 2 60 26 0. 026 4. 8 120 15. 5 0. 31 4. 8 120 15. 5 0. 31 4. 8120 15. 5 0. 31 7 60 35 0. 35 4 60 20 0. 20 3 60 15 0. 15 10 60 50 0. 5O5. 2 60 26 0. 26 10 60 50 0. 50 5. 2 60 26 0. 26 10 60 50 0. 50 5. 2 6026 0. 26 7.0 60 35 0. 35 4. 8 120 15. 5 0. 31 4. 8 240 15. 5 0. 62 4. 8480 15. 5 1. 24; 4. 8 120 15. 5 0. 31 2. 2 6O 14. 5 0. 145 5. 2 60 76 0.76

1 No dip in dipersion.

a Directly to chromium plate from basis nickel plate.

2 Eliminate steps (1), (2), and (3) in standard sequence. 4 Directly tochromium plate from basis nickel plate.

From Examples 1-38, it will be apparent that the novel process permitsattainment of unexpected results. For example by comparison of Example 8with control Example 9, it will be observed that the product chromiumplate prepared in practice of this invention exhibits 16,- 000 pores persquare centimeter, while the control exhibited no pores. It is entirelyunexpected that a chromi- 11m plate having a thickness of 0.065 micronwould have this degree of rnicroporosity; a normal commercial or priorart chromium plate of this thickness deposited over a bright nickelplate would exhibit a microporosity of essentially zero. A microporouschromium deposit is characterized by substantially improved corrosionresistance.

It will also be apparent, from a comparison of Example 13 with controlExample 16 that it may be possible to produce a chromium deposit of 0.5micron thickness which is characterized by the presence of 400microcracks per centimeter-the control Example 16 (typical of a normalprior art plate) exhibited 10 gross cracks per centimeter and nomicrocracks. A chromium plate characterized by the presence of at leastabout 100 microcracks per centimeter possesses substantially improvedcorrosion resistance.

In the following examples, Hull cell panels may be bright nickel plated,water rinsed, acid dipped, water rinsed, as were the panels for thefirst series of examples supra. The panels may then be dipped into anaqueous dispersion of talc (Mistron Monomix brand supplied by SierraTalc and Chemicals Inc.) having a maximum particle size of 6 microns anda median particle size of 1 micron. The basis metal, removed from thedispersion, and bearing a stratum of talc was then plated for 10 secondsin a standard commercially available bright nickel system. Currentdensity (C.D.) at varying points on the cathode was determined.

The matrix nickel plate containing talc particles was then withdrawnfrom the bright nickel plating bath, water rinsed, and chromium platedfor 60 seconds in a standard chromium plating bath containing 240 g./l.of chromium acid, 1.5 g./l. of sulfate (supplied as sodium sulfate),anld)2 g./l. of silicofluoride SiFF (supplied as the sodium sat Theproduct chromium plate was observed and the number of microcracks/ cm.or the number of pores/cm? was determined by standard techniques.

In Table IX infra, the noted procedure was followed for Example 39.Example 40 was conducted in a manner similar to Example 39, except thatthe basis metal bearing the stratum of particles was rinsed after thedip in the dispersion. In Example 42, there was added to the dispersant0.0012% of Hallcomid M-l8-01 (80% N,N- dimethyloleamide), C. P. Hall Co.of Illinois. In Example 43, the procedure of Example 39 was followedexcept that no matrix deposit was applied over the stratum of particles,this example thus serving as a control. l

TABLE IX Cone. 0.1). in N1 C.D.inCr

tale, matrix bath, bath, g./l. a.s.d. a.s.d.

Thousand pores/om.

n- H H H Jwcno wem o NnhQO M c-10 From Table D(, it will be apparentthat practice of the process of this invention permits attainment ofproduct chromium plate characterized by microcracking in desired amountat selected thickness and by microporosity at selected thickness. Moresignificantly, Table IX shows that it is possible to plate an entirepanel over a wide range of current densities and to obtain a chromiumplate which, at all normal decorative thicknesses, possesses either adesired microcrack pattern or a desired microporosity. This continuityof microcracking and microporosity permits attainment, over the entirearea, of a chromium plate having an unexpectedly high resistance tocorrosion. In practice prior art processes, if the plater tries toproduce microcracking over the entire area of a decorative chromiumplate, there are produced plated areas (e.g. intermediate currentdensity areas) which are neither microcracked nor microporous, butrather are undesirably characterized by gross cracking with attendantlow corrosion resistance and poor appearance.

The following examples serve to illustrate the advantages in corrosionresistance obtained by practice of this invention.

Steel panels were copper plated and buffed to produce a final layer ofbuffed copper of about 7.5 microns thick. They were then plated in abright nickel plating bath to produce a thickness of 25 microns. Exceptfor the control which was Water rinsed and plated in chromium, theothers were dipped in the noted dispersion, plated in a matrix bath ofWatts nickel for 10 seconds at 3 a.s.d and then plated in chromium.After 48 hours corrosion testing (CASS) the ratings were noted.

In Table X, the CASS rating is given as a pair of numbers wherein thefirst number indicates the degree of basis metal corrosion and thesecond number indicates the appearance. In each case, over a scale of to10, the higher numbers indicate a better rating; and values greater than7-8 may be acceptable. Thus the control row, which is illustrative ofthe range of thicknesses occurring over a normal decorative plate, isunsatisfactory because over the 0.125 and 0.25 micron areas thecorrosion ratings are 2/2 and 3/3 which are unacceptable. At the 0.50micron thickness, the undesirable gross cracking attained makes theplate unsatisfactory. In contrast, in the other two examples, themicro-perforations permit attainment of satisfactory plate at allthicknesses over the plated piece.

Although this invention has been illustrated by reference to specificexamples, numerous changes and modifications thereof which clearly fallwithin the scope of the invention will be apparent to those skilled inthe art.

I claim:

1. A process for preparing a metal plate receptive to a decorative noblemetal electrodeposit, characterized by the presence of microporous areasand microcracked areas over substantially the entire surface of saidnoble metal plate, comprising affixing to a basis material hearing aconductive metal surface a stratum of particles having a particle sizeof about 0.05-15 microns and a density on said conductive metal surfaceof about 100- 5,000,000 particles/cm. and then depositing in saidstratum of particles a conductive metal layer free of said particleshaving an effective thickness less than the maximum thickness of saidstratum of particles thereby forming a matrix wherein said particles areretained affixed to said surface in fixed position in said conductivemetal layer, and at least some of said particles intercept the surfaceof said conductive metal layer.

2. A process for preparing a metal plate receptive to a decorative noblemetal electrodeposit, characterized by the presence of microporous areasand microcracked areas over substantially the entire surface of saidnoble metal plate as claimed in claim 1 wherein said conductive metalsurface is a nickel surface.

3. A process for preparing a metal plate receptive to a decorative noblemetal electrodeposit, characterized by the presence of microporous areasand microcracked areas over substantially the entire surface of saidnoble metal plate as claimed in claim 1 wherein said density of saidparticles is 5,000-2,000,000 particles/cm? 4. A process for preparing ametal plate receptive to a decorative noble metal electrodeposit,characterized by the presence of microporous areas and microcrackedareas over substantially the entire surface of said noble metal plate asclaimed in claim 1 wherein said particles are platelet-shaped.

5. A process for preparing a metal plate receptive to a decorative noblemetal electrodeposit, characterized by the presence of microporous areasand microcracked areas over substantially the entire surface of saidnoble metal plate as claimed in claim 1 wherein said particles areaffixed to said conductive metal surface from a bath.

6. A process for preparing a metal plate receptive to a decorative noblemetal electrodeposit, characterized by the presence of microporous areasand microcracked areas over substantially the entire surface of saidnoble metal plate as claimed in claim 1 wherein said particles areaffixed to said conductive metal surface by dipping said basis materialinto a fluidized bed of said particles.

7. A process for preparing a metal plate receptive to a decorative noblemetal electrodeposit, characterized by the presence of microporous areasand microcracked areas over substantially the entire surface of saidnoble metal plate as claimed in claim 1 wherein said particles areparticulate material selected from the group consisting of talc, kaolin,wax, graphite, sulfide, pigments, plastics, diatomaceous earths,powdered aluminum, activated carbon, silicates, carbonates, carbides,sulfur, and mixtures of these materials.

8. A process for preparing a metal plate receptive to a decorative noblemetal electrodeposit, characterized by the presence of microporous areasand microcracked areas over substantially the entire surface of saidnoble metal plate as claimed in claim 7 wherein said particulatematerial is talc.

9. A 'process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble metal plate as claimed in claim 7 wherein said particulatematerial is graphite.

10. A process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble metal plate as claimed in claim 7 wherein said particulatematerial is molybdenum disulfide.

11. A process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble metal plate as claimed in claim 7 wherein said particulatematerial is tungsten disulfide.

12. A process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble 15 metal plate as claimed in claim 7 wherein said particulatematerial is latex plastic. 1

13. A process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble metal plate as claimed in claim 12 wherein said latex plasticis selected from the group consisting of butadiene-styrene copolymer,vinyl chloride polymer, vinyl acetate polymer and vinylidenechloride-acrylonitrile copolymer.

14. A process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble metal plate as claimed in claim 12 whereinv said latexplastic is acrylonitrile-butadiene-styrene terpolymer.

15. A process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble metal plate as claimedin claim '1 wherein said conductivemetal layer is selected from the group consisting of nickel, nickel-tin,cobalt, silver, rhodium, platinum, copper, bronze, brass, zinc, cadmiumand manganese.

16. A process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble metal plate as claimed in claim 15 wherein said conductivemetal layer is nickel.

17. A process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble metal plate as claimed in claim 1 wherein said efiectivethickness of said conductive metal layer is 0.02-3 micron;

18. A process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble metal plate as claimed in claim 1 wherein the actualthickness of said conductive metal layer is 20%200% of the maximumthickness of said stratum of particles whereby said effective thicknessof said conductive metal layer is less than said maximum thickness ofsaid stratum of particles.

19. A process for preparing a metal plate receptive to a decorativenoble metal electrodeposit, characterized by the presence of microporousareas and microcracked areas over substantially the entire surface ofsaid noble metal plate as claimed in claim 1 comprising affixing to abasis material bearing a conductive nickel surface a stratum of latexplastic particleshaving a particle size of about 0.05-15 microns and adensity of said conductive nickel surface of about 5,0002,000,000particles/cm. and then depositing in said stratum of latex plasticparticles a conductive nickel layer free of said particles having aneffective thickness of 0.02-3 microns, which effecttive thickness isless than the maximum thickness of said stratum of latex plasticparticles thereby forming a matrix wherein said latex plastic particlesare retained affixed to said surface in fixed position in saidconductive layer, and at least some of said particles intercept thesurface of said conductive nickel layer.

20. A process for preparing a decorative electrodeposited chromium platecharacterized by the presence of microporous areas and microcrackedareas over substantially the entire surface of said chromium plate,comprising afiixing to a basis material bearing a conductive metalsurface a stratum of particles having a particle size of about 0.05-15microns and a density on said conductive metal surface of about1005,000,000 particles/cm. then depositing in said stratum of particlesa conductive metal layer free of said particles having an effectivethickness less than the maximum thickness of said stratum of particlesthereby forming a matrix wherein said particles are retained affixed tosaid surface in fixed position in said conductive metal layer, and atleast some of said particles intercept the surface of said conductivemetal layer; and electrodepositing on said matrix a decorative chromiumplate whereby said chromium plate contains microporous areas andmicrocracked areas over substantially its entire surface.

References Cited UNITED STATES PATENTS JOHN H. MACK, Primary Examiner T.TUFARIELLO, Assistant Examiner US. Cl. X.R. (20438, 41

